Ferdinand has missed the last couple of weeks' action with Manchester United after picking up what was thought to be a calf injury.

However, it has now been confirmed the injury relates to a previous problem with his lower back.

The England defender will not be fit for tomorrow's Barclays Premier League encounter with Everton at Old Trafford, but the 31-year-old should be back in action soon.

"It is back related," Ferguson said. "We are not putting a timescale on it but it is not a situation where we are saying it will be months, it might be a couple of weeks or it might be a few weeks but that is it."

With Ferdinand out, Ferguson is relieved to have Nemanja Vidic available after he missed the defeat at Chelsea immediately before the international break with a calf problem.

However, Gary Neville is suspended and John O'Shea is almost certain to miss out with a thigh injury picked up in the Republic of Ireland's controversial World Cup exit in France on Wednesday.

Northern Ireland international Jonny Evans is a doubt as well, leaving Ferguson with some "patching up" to do in defence.